218 J. HOPKINSON THE CLIMA.TE OF ST. ALBANS. 



Pressure of the Atmosphere (Tables I-III, p. 219). — The mean 

 pressure was the same (29*990 ins.) during each half of the period. 

 The year of lowest pressure was not the wettest, nor was the year 

 of highest pressure the driest, in the series. Both these years were 

 in the second half of the period. 



Pressure was considerably above the mean in the first and the 

 last year of the series, appreciably below the mean in three years, 

 and the mean or very near it in five years The average annual 

 deviation from the mean was 0'023 in. AVhilst the lowe.st and the 

 highest mean annual pressures deviated almost equally from the 

 mean for the whole period, the lowest pressure recorded deviated 

 0-5 17 in. more from the mean than did the highest pressure, and 

 the mean of the lowest pressures deviated from it 0*441 in. more 

 than the mean of the highest pressures. 



The extreme range of pressure was 2"387 inches, being from 

 28-538 inches on 11th November, 1891, to 30-925 inches on 30th 

 January, 1896. 



On the average, pressure is low in spring and autumn, a little 

 higher, but still below the mean, in summer, and considerably 

 above the mean in winter. It is lowest in October and highest in 

 February. The season with the lowest mean pressure was the 

 spring of 1890 (29-8o6 ins.), and that with the highest the winter 

 of 1890-91 (30-226 ins.). The months with the lowest mean 

 pressure were February, 1893 (29-700 ins.), and October, 1889 

 (29'703 ins.) ; the month with the highest mean pressure was 

 February, 1891 (30-488 ins.). This was the month of least 

 rainfall. 



Temperattire of the Air (Tables IV- VI, p. 221). — The second 

 half of the period was about a degree warmer than the first half, 

 the mean temperature during the first five years being 47°-46, or 

 0°-53 below the mean for the period (47°-99), and during the 

 second five years, 48°-52, or 0°-53 above the mean, the difference 

 therefore being 1°*06. Both the coldest and the warmest year 

 occurred during the later period, 1892 being the coldest and 1893 

 the warmest, and giving an extreme annual range for the whole 

 period of 3°-3. No other years differ from each other in their 

 mean temperature so much as two degrees, and the annual average 

 deviation from the mean is 0°-65, the temperature being below the 

 mean in five years, above it in four, and equal to it in one year. 



The coldest year had no other special characteristics, but if the 

 9 a.m. temperature be taken into consideration, 1888 comes out as 

 the coldest, and that had the least daily range of temperature, the 

 most cloudy sky, much the fewest days of clear sky, and much the 

 largest number of days of overcast sky. The warmest year had the 

 greatest daily range of temperature, the cMest atmosphere, the 

 clearest sky, the greatest number of days of clear sky, and much 

 the smallest number of days of overcast sky. 



The extreme range of temperature was 80°-9, the absolute 

 minimum being 10°- 1 on 7th February, 1895, and the absolute 

 maximum 91°-0 on 18th August, 1893, 



